The invention relates to a steam turbine having an exhaust-steam casing.
A steam turbine is normally used in a power plant for driving a generator or in an industrial plant for driving a production machine. To this end, steam serving as flow medium is fed to the steam turbine and expands in the steam turbine to perform work. After its expansion, the steam normally passes via an exhaust-steam casing of the steam turbine into a condenser connected downstream of the latter and condenses there. In that case, flow may occur axially or also radially through the exhaust-steam casing. The condensate is then fed as feed water to a steam generator and passes after its evaporation into the steam turbine again, so that a closed water/steam loop is obtained.
The turbine casing of a steam turbine is normally composed of a plurality of casing sections which are adapted in their design dimensions to predetermined boundary parameters, such as, for example, the desired rating. In particular with regard to the advancing standardization and modularization in power plant construction, the casing sections can also be dimensioned for a suitable combination with other standard components.
A steam turbine with axial outflow is disclosed, for example, by Tremmel, Kachler, and Bourcier in xe2x80x9cEntwicklung einer kompakten 300-MW-Dampfturbine mit einflutigem ND-Teil und axialer Abstrxc3x6mungxe2x80x9d [Development of a compact 300 MW steam turbine with single-flow LP part and axial outflow], VGB Kraftwerkstechnik, 72, 1992, pp. 33-43. There, the exhaust steam flows through the exhaust-steam casing in a direction essentially parallel to the main axis of the turbine rotor. Such a concept may be advantageous and desirable, for example, especially for use in so-called gas-turbine and steam-turbine plants. In a steam turbine with axial outflow, the turbine rotor is normally mounted in an end bearing disposed inside the exhaust-steam casing and surrounded by an inner hub. In that case, the inner hub together with the outer jacket of the exhaust-steam casing forms a flow space of annular cross section for the exhaust steam. The flow space is normally configured as an annular diffuser virtually over the entire length of the exhaust-steam casing.
The exhaust-steam casing is normally arranged via an encircling radial flange on the casing section preceding it, which is also designated as inlet casing. With regard to its steam inflow region, the annular diffuser formed by the exhaust-steam casing is therefore largely fixed by the dimensions of the inlet casing. However, depending on the predetermined rating of the steam turbine and thus depending on the standard module selected for the inlet casing, these dimensions can vary to a comparatively large extent. On the other hand, the annular diffuser is fixed in its dimensions on the steam-outlet side by the connection diameter of the downstream condenser, which in turn, for reasons of standardization, is generally selected to be standardized irrespective of the rating of the steam turbine.
The adaptation of the exhaust-steam casing and of the annular diffuser formed at the same time to a combination of a standard module for the inlet casing with a standard module for the condenser, this combination ultimately being predetermined by the rating of the steam turbine, may therefore be comparatively complicated, especially as, on account of the functionality as a diffuser, special attention is to be paid to the configuration of the flow path. Such a complicated adaptation can largely offset the advantages which can be achieved by the modularization and/or standardization of the components.
The object of the present invention is to provide a steam turbine having an exhaust-steam casing and a turbine rotor mounted in an end bearing arranged inside the exhaust-steam casing and surrounded by an inner hub, which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this general kind, and in which steam turbine the exhaust-steam casing can be adapted with especially simple means to various combinations of inlet casing and condenser while maintaining favorable flow properties of the exhaust steam.
With the above and other objects in view there is provided, in accordance with the invention, a steam turbine, comprising:
a turbine rotor mounted in an end bearing;
an exhaust-steam casing enclosing the end bearing;
the exhaust-steam casing having an outer jacket formed of a first jacket part in a shape of a cylindrical jacket, a second jacket part in a shape of a conical jacket, and a stiffening ring connecting the first jacket part to the second jacket part;
a guide element in a shape of a conical jacket arranged on the stiffening ring and adapted to direct an exhaust-steam flow inside the outer jacket; and
an inner hub surrounding the end bearing, the inner hub comprising a first hub part substantially in a shape of a conical jacket and a second hub part substantially in a shape of a cylindrical jacket.
In accordance with a concomitant feature of the invention, the guide element extends on an inlet side thereof beyond a last moving-blade row of the steam turbine in a direction of flow of the exhaust steam.
In other words, the objects of the invention are achieved in that outer jacket of the exhaust-steam casing comprises a first jacket part in the shape of a cylindrical jacket, which is connected via a stiffening ring to a second jacket part in the shape of a conical jacket, a guide element in the shape of a conical jacket is arranged on the stiffening ring in order to direct the exhaust-steam flow inside the outer jacket, and in that the inner hub comprises a first hub part essentially in the shape of conical jacket and a second hub part essentially in the shape of a cylindrical jacket.
The invention is based on the idea that extensive use of standard components, while ensuring high flexibility in the configuration of the flow passage, should be provided for an especially simple adaptation of the exhaust-steam casing to any desired combination of inlet casing and condenser. The standard components provided in this case are, in particular, the first jacket part in the shape of a cylindrical jacket and the second jacket part in the shape of a conical jacket. Here, the first jacket part is provided for a connection to the radial flange of the inlet casing, which radial flange may be designed in standard dimensions irrespective of the rating of the steam turbine. The second jacket part, on the other hand, is provided for the connection to the condenser and, in accordance with the normally standardized dimensioning of the latter, is likewise designed in standard dimensions. In this case, the conical-jacket-shaped design of the second jacket part assists its use in the diffuser region. At the same time, the guide element together with the second jacket part in the outer region and the inner hub in the inner region form a diffuser of annular cross section, which can be designed in a simple manner for an especially favorable flow behavior, in particular by suitable dimensioning of the first hub part in the shape of a conical jacket.
The rating-dependent adaptation is then effected in a comparatively simple manner by the guide element in the shape of a conical jacket, which is arranged inside the first jacket part and limits the inflow cross section for the steam to the selected outlet cross section of the upstream inlet casing.
The guide element expediently extends on the inlet side beyond the last moving-blade row as viewed in the direction of flow of the exhaust steam. In this way, an especially favorable fluidic transition from the inlet casing into the outflow region can be achieved, so that the diffuser function is ensured in an especially reliable manner.
The advantages achieved with the invention consist in particular in the fact that the first and second jacket parts of the outer jacket enable the exhaust-steam casing to be connected to both the upstream inlet casing and the downstream condenser in an especially simple manner via standard components, an adaptation to the inlet casing specifically selected in accordance with the required rating being ensured by the guide element. In addition, fluidically favorable shaping of the flow region is achieved by the guide element, in which case a reliably acting annular diffuser can be formed especially in combination with that part of the inner hub which is in the shape of a conical jacket, even when the flow geometry of the inlet casing varies.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a steam turbine having an exhaust-steam casing, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.